WASHINGTON – A former New York prosecutor who has the ear of President Bush is being discussed by Republican insiders as a potential replacement for the Secretary of Homeland Security, Tom Ridge, should he resign.

Long Island native Frances Fragos Townsend cut her teeth prosecuting organized crime under Rudolph Giuliani and was a deputy to Clinton Attorney General Janet Reno before becoming a close counterterrorism adviser to Mr. Bush.

Two other New Yorkers considered top candidates for the job – Governor Pataki and Mr. Giuliani – have said they are not interested in moving to the capital. Another frequently mentioned name to replace Mr. Ridge is the undersecretary for border and transportation security, Asa Hutchinson.

While the list also includes several prominent governors with presidential ambitions, Ms. Townsend is highly regarded by the president and is well liked by his national security adviser, Condoleezza Rice, according to people who know them.

A Long Island Republican, Rep. Peter King, who sits on the House Select Homeland Security Committee, said she would be a “great” pick.

“She’s got that absolute intensity that is needed in the job,” Mr. King said.

The choice of Ms. Townsend would be consistent with Mr. Bush’s second term appointments to date.

“They have all been insiders who are already on board with the agenda and who have his trust and confidence,” said a senior research fellow in defense and homeland security at the Heritage Foundation, James Carafano.

“I don’t think that anybody could question whether she will be in synch with the priorities and interests of the president, and that he will have anything less than total faith and confidence in her,” he said.

Appointed the president’s homeland security adviser last May at the age of 42, Ms. Townsend provides regular briefings in the Oval Office, and she presides over meetings of top Cabinet secretaries in the Homeland Security Council. She has also led a task force on terrorist financing, making several trips to Saudi Arabia to press for cooperation in the war on terror.

Some conservatives initially criticized her appointment because she had worked closely with Ms. Reno while she was a lawyer in the Justice Department.

Ms. Townsend has been quoted as saying she is a lifelong registered Republican.

Ms. Townsend began her career as an assistant district attorney in Brooklyn in 1985, and three years later she was hired by then-U.S. Attorney Mr. Giuliani to specialize in international organized crime and white-collar crimes.

She later moved to Washington, serving as a deputy to Ms. Reno and working on international law enforcement. In 1998, she took over the Office of Intelligence Policy and Review at Justice, which reviews FBI requests for secret surveillance of terrorists.

She also served as deputy national security adviser for combating terrorism, replacing Richard Clarke, who penned a best-selling book blasting the president for failing to take terrorism seriously in his first nine months in office.

Ms. Townsend worked closely with the late deputy FBI director, John O’Neill, who resigned his job after arguing – before the September 11 attacks – that the administration was moving too slowly to destroy Al Qaeda. O’Neill was killed in the World Trade Center attacks.

From her perch at the White House, Ms. Townsend has seen firsthand some of the challenges the young department has faced, said a former colleague, Paul Kurtz, who worked with her as member of the Homeland Security Council in the Bush administration, and in the Justice Department under President Clinton.

“She has worked it hard for the past couple of years. She’s got the background to fix the problem,” said Mr. Kurtz, now the executive director of the Cyber Security Industry Alliance, a lobbying group.

Ms. Townsend’s style is one of “asking tough questions and cutting through the BS,” he said.

Despite heavy speculation that he plans to leave, Mr. Ridge has not announced his intentions. Some observers expect him to stay in the post to oversee the security of the inauguration in January.

His successor faces reviewing and building on the structures that have been created by Mr. Ridge to ensure practical cooperation between agencies involved in border control and law enforcement.

“We’ve done a great job of setting up the department. We’ve put on the bones, and now we need to put on the muscles,” said a senior legal research fellow at the Heritage Foundation, Paul Rosenzweig.